Effect of light level on colour appearance

Abstract

Colour perception is a perceptual response of the human visual system to stimuli with different spectral compositions under different viewing conditions. The characterization of the perceived colour appearance is critically important to different applications, such as lighting, camera, and imaging systems. Great efforts have been made to develop numerical models (e.g., colour appearance models and uniform colour spaces) for colour specification, colour reproduction, and characterization of light source colour rendition. These models were developed and verified through psychophysical experiments which were carried out under a limited number of standard illuminants and a small range of light levels for general illumination. Therefore, these models may not be applicable to the requirements of modern technologies and the stronger desires to achieve accurate colour reproduction across a wide range of conditions. This dissertation reports a series of psychophysical experiments that were designed to test hypotheses that light level should be considered in specifying light source colour rendition, and the existing models (i.e., CIECAM02) cannot accurately characterize the colour appearance of stimuli under a wide range of light levels. The results clearly suggested the importance of light level in specifying light source colour rendition. The source that can achieve a greater chroma enhancement was generally preferred under a lower light level, while the one with little chroma enhancement was preferred under the extremely high light levels. Based on this, CIECAM02 was found to have bad performance in characterizing the colour appearance of stimuli under these extremely high light levels, and the adapting light level was recommended to be considered to better characterize the colour attributes. Lastly, a carefully designed experiment was carried out to test and verify the performance of CIECAM02 in characterizing unique hues and hue linearity. In summary, this dissertation helps us to better understand how various factors should be considered in characterizing the colour appearance of stimuli under various viewing conditions. The findings also suggest the necessary improvements and considerations for colour characterization and reproduction.